Northwest Michigan fruit regional report – May 21, 2013

Hot temperatures over the weekend brought isolated storms across the region on Monday, May 20. Growers are concerned about disease development under these optimal conditions.

Temperatures made it seem like July over the weekend when we hit 80s to mid-80s on Sunday (May 19) and Monday, and nighttime temperatures dropped only into the high 60s and low 70s. With these warm temperatures and the forecasted rainfall, growers have been spraying through the weekend and into Monday (May 20) to prevent disease development; fire blight is of particular concern under these conditions.

With the recent warm temperatures, we have accumulated growing degree days (GDD) and we are now right on target with our 20-plus-year average. So far this season we have accumulated 420 GDD base 42 (average: 462 GDD base 42) and 232 GDD base 50 (average: 219 GDD base 50). The region also received variable rainfall yesterday (May 20) and more rain is predicted for today and tomorrow. Yesterday’s rains were isolated and many of the storms were short-lived, but powerful. We have had reports of hail south of Elk Rapids, Mich., and in Traverse City, Mich., and many growers re-applied fire blight sprays to damaged apples in locations with a past history of fire blight.

Apples. As mentioned above, fire blight is the disease of concern in apples at this time. Growers have been making applications to control this disease and keeping a close eye on the radar, weather conditions and the fire blight model on Enviro-weather.

The weather forecasts seem to be all over the board, and it has been difficult to make decisions with this “moving” target. The high chance of rain yesterday resulted in isolated showers and storms, which was unlike the original forecast of rainfall throughout the region. Michigan State University Extension advises growers that sprayed for fire blight on Sunday should reapply today (May 21) to make it through the next two days of rain and heat. By Thursday (May 23), temperatures will drop and fire blight will not be as much of a concern on opening blossoms. The temperatures on Thursday and into Memorial Day weekend are predicted to be in the 50s, which is not conducive for the fire blight pathogen, but these cool conditions are a concern for honey bee flight for pollination.

Scab is a concern with the fast growing new tissue, and with the warm temperatures and rain, this new growth will need to be covered. We have caught an average of 125 spotted tentiform leafminers per trap this week in apples. No codling moths have been caught in the region.

Cherries. Warm and humid conditions are conducive for the American brown rot pathogen. Although here at the Northwest Michigan Horticultural Research Station we are in petal fall/shuck split in sweet cherries, orchards to the north may still have open sweet cherry bloom and growers should consider adding an American brown rot fungicide to their next Bravo/chlorothalonil sprays.

These conditions are also good for cherry leaf spot development, and although the model is not yet predicting a cherry leaf spot infection, the open bract leaves on Montmorency and Balatons have open stomates and can be infected by cherry leaf spot spores. Despite their small size, these leaves should be covered at this time. Last year (2012), we had epidemic levels of cherry leaf spot in orchards where bract leaves were infected early in the season. Growers need to be sure to read all labels closely when tightening up fungicide application intervals with the warm and rainy weather.

No obliquebanded leafrollers have been detected in sweet or tart cherry orchards. American plum borers have begun flying, and we caught an average of 6.5 moths per trap this week. Green fruitworm moths have also been trapped.

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